After I posted this recipe, I had a good friend, Gerardo de la Fuente, from Monterrey ot Los Angeles, Mexico message me. He explained to me that altitude plays a big part in whether you need baking powder or not. If you are 1,000 m below sea level, like in Monterrey, no baking powder is needed for soft flour tortillas. Baking powder will tend to harden tortillas as they get cold in this case. But if you are 1,000 m above sea level, like in CDMX or Guadalajara, baking powder is ideal for soft tortillas.